Program

Question

int main()

    {
    char ch=1;

    while(ch<256)
    ch++;

    printf("Loop end");

    return 0;
    }

what will be output?

Comments

I think it will print only one time as loop end .

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but I don't think loop is going to end, because 

while(ch<256)ch++;

This will go in infinite loop until memory stack is full.

ch= 1, 2, 3, ......, 255, 0, 1,......, 255, 0,.............

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Right, it will execute infinite loop.

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@vijaycs  I did not get , how following piece of code

while(ch<256)ch++;

exhaust stack ?

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@Debashish, It is infinite loop. Soon, stack will overflow.

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Is not there a difference between infinite loop and stackoverflow error? what I know stackoverlflow error arise because of deep recursion.

example: Simply

while(1) a=x;

will not cause stackoverflow. My point is the program in the given question never stop running. 

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@Debashish,

A recursive call leading to non terminating deep recursion will definitely lead to stack overflow.

But , every stack overflow is not caused by a recursive call .This is an infinitely loop, which cannot be recovered till stack overflows or time limit exceeds.

Answer 1

Char is 1 Byte. There are three distinct types of char in c99 standard. 

char , signed char,unsigned char

default char can be either signed or unsigned. It is implementation specific.For gcc, the default is signed.

In decimal notation value of a signed char can vary from $+(2^{n-1} -1)$ to $-(2^{n-1})$

which is (+127 to -128).

So after ch becomes 127 (01111111) then ch++ makes the value to (10000000) = -128 (2's complement form)

=> ch values rotate between (127  to -128). While condition always satisfied.

=> INF loop. nothing printed.

--------------------------------

In gcc we can use -funsigned-char flag during compilation time  which makes default char unsigned.

Now char range becomes (0 to +255) i.e. if ch = 255 at some point, ch++ makes ch=0

=> ch values rotate between (0 to +255), While condition always satisfied.

=> INF loop. nothing printed.

--------------------------------

conclusion : irrespective of implementation of default char sign (signed/unsigned). Nothing will be printed.

Answer 2

Range of character varies from machine to machine...lets us take it as 1 byte..so the range of character is from -128 to +127 as msb is used for signed..

so ch get value 1 and then increamented till 127 and in the next itteration it will again -128 which will obviously<256 ,so it will go to infinite loop and thus "Loop end "will not be printed.

p.s-:please insert  check printf"hello"  inside the while loop which will verify you the infinite loop